Plastic containers, and especially plastic bottles, have a neck the dimensions of which are precisely defined and remain unchanged during the manufacturing operations. Most handling machines include transfer devices such as transfer wheels provided at their periphery with a plurality of neck grippers or clamps configured to receive and hold the containers by their necks.
There exist several types of clamp designs. According to the most common design, the clamp comprises a pair of arms hinged with respect of each other, the angular position of which is controlled e.g. by cam means including a fixed cam path interacting with a movable cam follower provided on one of the arms, in such a way that when reaching a loading point the arms open to allow a container neck to be received therebetween. A compression spring is interposed between the arms to bias them towards each other against the opening force exerted by the cam means. For further details, one can refer to European patent application No. EP 1 867 600 (Sidel). Such a design has been in use in the container handling industry for years, and has given proof of its precision and smooth operation.
However, clamps of that type have drawbacks, due to the important number of numerous moving parts they include, which not only increases their manufacturing costs and their setting time, but also creates problems of reliability due to wear and setting defaults.
Therefore, alternate designs have been sought. One solution consists in providing a one-piece clamp having resilient arms, which elastically open under pressure of a container neck being received radially during a transfer operation. In theory, such a clamp, disclosed in Japanese patent application No. JP 2001-287795 (Masaaki), seems to overcome the drawbacks of the ordinary clamps, for it is no more necessary to provide cam or other means to positively open the arms in order to allow reception of the container necks. In practice however, such a clamp proves to give satisfaction in static conditions only, i.e. when the container is received radially between the arms, that is along the axis of symmetry of the clamp. Transfer devices do not work that way, though, for containers move along arc-of-circle paths and are transferred from one clamp to another in a tangential way, in a transfer area where the periphery of the two adjacent star wheels locally overlap. More precisely, as the arms are not open when they come in contact with the container neck, the distance between the gripping jaws of the arms at the radial end thereof may be too short for the container to smoothly and easily force its way between the arms. The skilled person may increase that distance, which can be achieved by reducing the angular opening of each gripping jaw. However such a solution is not satisfactory because, on the other hand, the angular opening of each gripping jaw should be set a maximum value to ensure sufficient—and therefore safe—enclosure of the container during its arc-of-circle path on the transfer wheel, along which path strong centrifugal forces apply, which tend to force the container out of the clamp.
One further and common drawback of the hereabove disclosed clamps of both types is that they do not (at least, not easily) adapt to several container formats, i.e. to different diameters of container necks. In particular, should the clamp according to Japanese patent application No. JP 2001-287795 receive a neck of a diameter larger than the one depicted on the drawings, would the clamp open at such an angle to let the container escape therefrom under the centrifugal forces during rotation of the transfer wheel.